This invention relates to a pressure control valve for a vehicle hydraulic brake system including a first brake circuit associated with the front wheels and a second brake circuit associated with the rear wheels, wherein the wheel brake cylinders of the first brake circuit are connected with a first pressure chamber of a master cylinder and the wheel brake cylinders of the second brake circuit are connected with a regulator outlet chamber of the pressure control valve with a regulator inlet chamber of the pressure control valve being connected to a second pressure chamber of the master cylinder, and a valve is arranged in a fluid pressure line between the inlet and outlet chamber, the valve having a closure member on which a control piston acts which is preloaded by a spring and has one surface subjected to the pressure of the first brake circuit.
From German Pat. No. 1,958,398 a brake pressure control valve is known by means of which the pressure increase in the brake circuit associated with the rear wheels is reduced above a predetermined change-over pressure. The brake pressure control valve includes a stepped piston which is slidable against a control spring and opens or closes the valve. The valve closure member is arranged interiorly of the stepped piston and includes a tappet bearing against a pin. The pin is secured to a piston which is subjected to the pressure of the brake circuit associated with the front wheels and slidable against a second spring. In the presence of pressure in the front wheel brake circuit, the piston and thus the pin are displaced against the spring, and the pin releases the valve closure member. At the same time, the rear wheel brake circuit is pressurized, too, and when a predetermined pressure has been attained the stepped piston is displaced and the valve is closed. In the event of failure of the front wheel brake circuit, the pin is not diplaced and therefore does not release the valve closure member, i.e., the pressure in the rear wheel brake circuit increases unreduced.
The known arrangement which has proved efficient because of its safe function includes a great number of individual components which results in high material and assembly costs.